Conventionally, carbon black is produced by burning a carbonaceous material in the presence of a combustion-supporting material in a highly specialized furnace or reactor, terminating the burning after a relatively short residence time by the addition of a quench fluid to produce a hot combustion gas containing carbon black, preferably recovering heat values from the hot combustion gas by passing the same in indirect heat exchange with water and/or one or more of the reactant materials to produce a combustion gas of reduced temperature, and recovering the carbon black from the combustion gas of reduced temperature.
In one mode of operation, water is utilized as a quench fluid to terminate the burning. This quench water together with water produced in the burning step creates serious corrosion problems in equipment for recovering heat values from the hot combustion gas, as well as in the system for recovering the carbon black from the combustion gas of reduced temperature. This problem is particularly significant during start-up of the carbon black process. Normally, during start-up, a fuel gas is burned in the presence of the combustion-supporting material and all equipment downstream of the reactor is operated as it would conventionally be operated for the production of carbon black for a period of time sufficient to attain carbon black production temperatures in the equipment throughout the system. Thereafter, the feed material is substituted for part or all of the fuel gas and carbon black is recovered under production conditions. This line-out or start-up of the system is a rather lengthy procedure and the water utilized as a quench fluid as well, as that produced during the burning step, will condense on the metal parts of the equipment downstream of the reactor until the equipment reaches a temperature above the dew point of water and, of course, severe corrosion occurs.
In order to eliminate the problem of corrosion created by the use of water as a quench fluid and the additional equipment necessary for the utilization of water as a quench fluid, an alternative method is to withdraw a part of the combustion gas of reduced temperature after the recovery of heat values therefrom and before the introduction thereof to the carbon black recovery equipment, and utilize this combustion gas of reduced temperature as the quench fluid. While this procedure eliminates a substantial portion of the corrosion problem, there is still sufficient water in the hot combustion gas from the reactor to cause corrosion problems. In addition, one or more blowers must be utilized to recycle the combustion gas of reduced temperature to the reactor, as a quench. This adds additional equipment which will be subject to corrosion. Start-up by this method is also a lengthy proposition, requiring about one and one-half hours. Further, since the combustion gas of reduced temperature, normally utilized as a quench fluid during carbon black production, is substantially below operating temperature during this start-up period, it is conventional practice to utilize water as a quench fluid during the start-up period and, thereafter, substitute the combustion gas of reduced temperature. Finally, the blowers utilized to recycle the combustion gas of reduced temperature, as a quench fluid, are designed to operate at a predetermined temperature, which of course is the temperature of the combustion gas of reduced temperature during the production of carbon black. Therefore, these blowers must be operated at the pre-determined temperature in order to eliminate maintenance problems. For this reason also, water is utilized as the quench fluid during start-up until the recycle combustion gas to be utilized as a quench fluid reaches the predetermined temperature.